1. Field
Example embodiments relate to an organic memory device and a method for fabricating the memory device. Other example embodiments relate to an organic memory device including an ion transfer layer formed between a first electrode and a second electrode, and a method for fabricating the organic memory device.
2. Description of the Related Art
Recent developments in data compression and transmission technologies have led to increased use of digital media. Under such circumstances, types of electronic devices, including mobile terminals, smart cards, electronic money, digital cameras, game memories, MP3 players and/or multimedia players are continuously being developed. Because development of these electronic devices requires an increase in the amount of data that may be stored in memory devices, demand for a variety of memory devices has been increasing. With growing use of portable digital devices, memory devices may be required to ensure non-volatility so that written data is not erased even when the power is cut off.
Most currently available nonvolatile memories are flash memories based on silicon materials. However, silicon-based memory devices have fundamental physical limitations. Conventional flash memories have technical limitations in that the number of writing/erasing cycles is limited, the writing speed is slower, the production costs of memory chips are increased due to additional microprocessing for higher density of memory capacity, and chips may not be miniaturized any further due to technical difficulties.
In view of these technical limitations of conventional flash memories, efforts have been made to develop next-generation nonvolatile memory devices that overcome physical limitations of the conventional silicon-based memory devices and have the advantages of higher speed, higher capacity, lower power consumption and lower price. Next-generation memories may be divided into ferroelectric RAMs, magnetic RAMs, phase change RAMs, nanotube memories, holographic memories and/or organic memories, depending on constituent materials of cells, which are basic internal units of semiconductors.
Of these, organic memories may be devices including a memory layer formed of an organic material between an upper electrode and a lower electrode wherein memory characteristics are realized by using bistability of resistance values obtained when a voltage is applied between the upper and lower electrodes. According to the organic memories, bistability characteristics may be provided by cells formed at intersections between the upper and lower electrodes. The organic memories are devices wherein resistance values of the organic material present between the upper and lower electrodes may be reversibly varied by electrical signals so that data, e.g. “0” and “1”, may be written and read. Such organic memories have attracted much attention in recent years as next-generation memories because they may realize non-volatility, which is an advantage of conventional flash memories, and at the same time, may overcome the disadvantages of lower processability, higher fabrication costs and a lower degree of integration.
The conventional art includes an organic memory using 7,7,8,8-tetracyano-p-quinodimethane (CuTCNQ), which is an organometallic charge transfer complex compound. Further, a conventional semiconductor device may include an upper electrode, a lower electrode and an intermediate layer formed therebetween wherein the intermediate layer may be formed of a mixture of an ionic salt, e.g., NaCl and/or CsCl, and an electrically conductive polymer.
Further, a conventional organic memory device may include organic active layers and a metal nanocluster applied between the organic active layers. However, the problems of the device are that the yield is lower and the metal nanocluster is not uniformly formed.
On the other hand, metal filament memories are currently being investigated as structures of memories. According to the metal filament memories, resistance values may be varied by the formation and short-circuiting of metal filaments within an organic active layer between two electrodes. The advantages of such metal filament memories are lower price, possible three-dimensional stacking structures, longer retention time, improved thermal stability, and applicability to flexible memory devices. For example, polystyrene films formed from styrene vapor by a glow discharge polymerization technique are known to show memory characteristics due to the formation of metal filaments. However, no metal filaments may be formed within polystyrene films formed by a coating technique, e.g., spin coating.
Because the conventional metal filament memories include an organic active layer formed by vacuum evaporation, the fabrication processing may be complicated and considerable fabrication costs may be incurred. In addition, the problems of the conventional metal filament memories may be higher operating voltage and relatively difficult control of on/off current ratio.